That's a common Athiest belief, and doesn't hold up to even the most cursory of examinations. It typically devolves into a numbers fight, with casualty counts from Socialist/Communist lead killing programs vs religious wars, but even that misses the point.
Men fight and kill regardless of the presence of religion. I'd invite you to read "The Dark Side of Man" https://www.amazon.com/Dark-Side-Man-Helix-Books/dp/0738203157 and see the roots of violence, from wars to individual killing, and how completely necessary it has been in the development of mankind. Apes fight wars and murder, and as best we can tell they have no religion. They fight for the same reason we do, for resources. Religion (and state) are often used as excuses for resource wars, but all wars are resource wars at their most basic level. Religion is often a cover, a window dressing justification, but even the Crusades were not truly about religion any more than European incursion into "Native America" was really about converting the "savages" to Christianity. It's just a nicer way of saying "we want their land" or "I need to consolidate political and economic power".
If God's only son was murdered for political beliefs (claimed to be a king) and not for our sins, I'll concede that wars aren't religiously responsible.
Regardless, I'll read the book and thank you for offering the link.